As is well known, radioactive materials are used extensively in industrial, medical, agricultural, and environmental activities, among others. For example, radioactive waste is generated at nuclear facilities, and there are a number of liquid processes and waste streams at nuclear facilities that require treatment for removal of radioactive contaminants. Management of this waste typically includes treatment, temporary storage, and transportation of the waste to a permanent disposal site.
For example, the Savannah River Site (SRS) and the Hanford Site are nuclear reservations owned by the U.S. Department of Energy (DOE) and located in the states of South Carolina and Washington, respectively. The liquid waste operations contracts at these sites are respectively held by Savannah River Remediation (SRR) and Washington River Protection Solutions (WRPS), which are teams of companies led by the URS Corporation. A major focus of these contracts is cleanup activities related to work done in the past at these sites.
In particular, large, highly toxic quantities of high-level radioactive waste are located on the SRS and Hanford sites. At SRS, almost 40 million gallons of this waste, containing hundreds of millions of curies, is found in the form of sludge, salt, and liquid. Predominant radionuclides are plutonium, strontium-90, and cesium-137. Strontium and cesium account for more than 95% of the radioactivity. Large amounts of transuranic (TRU) waste are also stored on site. At Hanford, almost 60 million gallons of similar waste exists.
The current plan to deal with this waste is to first pretreat the waste via regenerable ion exchange at Hanford and liquid-liquid solvent extraction and non-regenerable ion exchange at SRS to remove various radionuclides. As is known, regenerable ion exchange and solvent extraction are effective for transferring the radioactive content of a large volume of liquid into a small volume of eluate and strip effluent, respectively, and non-regenerable ion exchange is effective for transferring the radioactive content of a large volume of liquid into a small volume of solid. Although ion exchange processes may be implemented in a variety of ways, the most common uses of ion exchange media are as packed beds in vessels. More particularly, an ion exchange medium is typically contained inside a stainless steel pressure vessel, with an engineered inlet, outlet, and flow distribution system to allow liquid to percolate uniformly through the bed of the medium at a specified flow rate. Many types of ion exchange media are available for this purpose, including inorganic and synthetic organic medias.
Secondary waste from the ion exchange or solvent extraction processes at Hanford at SRS is eventually mixed with precipitated solids and immobilized through a process called vitrification. Glass forming materials will be added to the waste at high temperature to form molten glass. The molten material will then be poured into stainless steel containers, where the glass will harden as it cools. The waste will still be radioactive, but no longer mobile (and thus not able to easily spread into the environment). At SRS, a vitrification facility called the Defense Waste Processing Facility (DWPF) has been operating for the past 15 years, with an operating expense of approximately one million dollars a day. During this time period, the waste volume and sludge volumes in the tanks have actually increased because of an insufficient capacity to treat liquid waste. At Hanford, a vitrification facility called the Waste Treatment Plant (WTP) has been under construction for the past eleven years but is not expected to begin operations until at least 2019 or beyond. Unfortunately, Hanford has multiple leaking tanks that require processing prior to the operation of the vitrification process.